Core wound paper products are in constant use in daily life. Particularly, toilet tissue and paper towels have become a staple in home and industry. Such products usually comprise a roll of a paper product spirally wrapped around a hollow core.
The hollow cores are typically made on a coremaking line and comprise inner and outer plies of paperboard superimposed in face-to-face relationship. Each ply of the paperboard is supplied to a coremaking mandril from a spool of raw material. When the two plies are fed to the coremaking mandril, they are typically helically wrapped in the same direction. During wrapping, the plies are adhered throughout to maintain the desired cylindrical configuration.
During converting, the cores are telescoped onto a mandril for subsequent processing--such as winding the paper product therearound. The mandrils are rapidly accelerated, which often causes the cores to burst. Core bursting is the phenomenon which describes a core rupturing on a mandril and disintegrating into strips of paperboard.
Core bursting cause two problems. First, there is a significant loss in efficiency as the mandril must be cleaned and restarted again and again until it runs smoothly and without core bursting occurrences. Secondly, each occurrence of core bursting causes material to be scrapped and increases manufacturing costs due to the excess of raw materials necessary to support each startup.
Of course, any time one desires to reduce material costs of the core, the first solution which comes to mind is to reducing the amount of materials used in the construction of the core. However, this "solution" has the drawback of further weakening the core, making it more susceptible to core bursting on the converting mandril--and the cycle repeats itself
If the core survives the converting mandril, there are other occasions where the properties of the core may cause it to be damaged before the core (and the paper product wound therearound) reach the consumer. For example, if the side to side (diametrical) crush strength of the core is not great enough, the core may collapse and cause the converting line to jam. In the converting line, cores are horizontally stacked several feet high in a converting bin. The converting bin has a trap door at the bottom which opens to feed the cores onto the line. The cores at the bottom of the converting bin must resist being crushed by the cores above while stacked in the bin and while fed into the line. If a core does not have sufficient side to side crush resistance, it will crush either blocking the cores from dumping into the converting line or will jam while in the line. In either occurrence, the converting line will incur a shutdown to clear the jam. Of course, the crushed cores must be discarded after they are cleared from the converting bin.
Assuming the core survives the converting mandril (and the balance of the line) without exploding the core is shipped with product wound therearound to a warehouse, where the cores are typically axially stacked in their cases. The cases of product wrapped cores are stacked several feet high in a warehouse and often are subjected to an axial compressive force in excess of 300 pounds. The cores at the bottom of the stacks must have sufficient crush strength to resist this axial compressive force, otherwise they will be crushed and the product may be too damaged to sell. Furthermore, if the cores at the bottom of the pallets are crushed, often gross deformation of these products occurs and the cases stacked near the top of the pallet fall over and are also damaged.
Accordingly, it is an object of this invention to reduce the material costs associated with making cores for core wound paper products. Furthermore, it is an object of this invention to increase the efficiency and speed at which the cores can be manufactured. Finally, it is an object of this invention to provide such cores having improved physical properties.